1. Field of the Invention
The present invention relates generally to the field of optical communications systems, and more particularly to systems and methods that employ semiconductor lasers in a free space environment.
2. Background of the Invention
An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. Isolators are typically used to prevent un-wanted feedback into an optical oscillator. The operation of the isolator depends on the Faraday Effect (which in turn is produced by magneto-optic effects), which is used in a Faraday rotator. A magnetic field, B, applied to the Faraday rotator causes a rotation in the polarization of the light due to the Faraday Effect. The angle of the rotation, .beta. is given by, .beta.=vBd, where v is the Vedet constant of the material that the rotator is made from, and d is the length of the rotator.
A polarization dependent isolator is made of three parts, an input polarizer, a Faraday rotator, and an output polarizer, wherein the input polarizer is polarized vertically and the output polarizer is polarized at 45 degrees. Light traveling in the forward direction becomes polarized vertically by the input polarizer. The Faraday rotator rotates the polarization of the light by 45 degrees, enabling light to be transmitted through the isolator. Alternatively, light traveling in the reverse direction becomes polarized at 45 degrees by the analyzer wherein the Faraday rotator rotates the polarization by 45 degrees. In other words, the light is polarized horizontally and since the polarizer is vertically aligned, the light will be extinguished.
An important optical element in an isolator is the Faraday rotator. The characteristics include a high Verdet constant, low absorption coefficient, low non-linear refractive index, and high damage threshold. The polarization rotation due to the Faraday rotator is always in the same relative direction. In the forward direction, the rotation is positive 45 degrees and, in the reverse direction, the rotation is negative 45 degrees. Therefore, when the light travels in the forward and reverse directions, a rotation of 90 degrees is achieved and higher isolation is comparable.
Optical isolators are used in optical communication systems, and especially used with semiconductor lasers. As the transmission rates used in optical communications systems have increased, the performance required of lasers used in such systems has also increased.
It is well known that light reflected back from some parts of an optical communications system will adversely affect the operation in high performance lasers. Such adverse affects include fluctuations in the spectrum, line width, or intrinsic noise of the laser.
Therefore, what is desired is an optical isolator(s) that protects high performance semiconductor lasers from reflections and limit un-wanted positional changes of an optical isolator element within a free space isolator design by decreasing deficiencies from movements of the optical isolator element.